The present invention relates generally to a protection circuit more specifically, the present invention relates to a 0-10V interface protection circuit.
As illustrated in FIG. 1, the output of many ballast-driven lighting systems can be controlled by employing an industry standard 0-10V dimmer. During the installation of 0-10V dimming ballasts, one of the commonly made mistakes is that the dimming input wires, together with the line input wires, are connected to the mains, which predictably results in damage to the dimming interface circuit inside the ballast. A protection circuit which protects the dimming interface circuit from being damaged when the dimming wires are wrongly connected is known. However, the known protective circuit sets the ballast at fill light output. Thus, although the interface circuit is protected from excess current/power, the user is not alerted to the fact that the system has been incorrectly wired.
Thus, when the dimming input wires, together with the line input wires, are connected to the mains, fill light output does not provide enough warning of the incorrect wiring. What is needed is a device which clamps the ballast at the lowest light output level when the dimming wires and the line input wires are incorrectly connected to the mains to thereby provide a positive indication of incorrect wiring. What is also needed is a protective circuit which provides the above-described protective function at low cost. It would be beneficial if the postulated protective circuit would include one or more current limiting elements.
Based on the above and foregoing, it can be appreciated that there presently exists a need in the art for a 0-10V dimming interface protection circuit which overcomes the above-described deficiencies. The present invention was motivated by a desire to overcome the drawbacks and shortcomings of the presently available technology, and thereby fulfill this need in the art.
One object of the present invention is to provide a dimming interface protective circuit which clamps the ballast at the lowest light output level when the dimming wires and the line input wires are incorrectly connected to the mains voltage to thereby provide a positive indication of incorrect wiring.
Another object according to the present invention is to produce a dimming interface protective circuit which provides the above-described protective function at a low cost.
Still another object according to the present invention is to provide a dimming interface protective circuit which provides the above-described protective function at a low cost by utilizing one or more current limiting elements.
These and other objects, features and advantages according to the present invention are provided by a circuit protecting a low voltage component from application of high voltages. Advantageously, the circuit includes a positive temperature coefficient (PTC) thermistor connected to one lead of the low voltage component, a voltage detector which detects application of the high voltages to the low voltage component and generates a control signal, and a switch operated responsive to the control signal. According to an aspect of the present invention, operation of the switch increases resistance of the PTC thermistor to thereby limit current to the low voltage component.
These and other objects, features and advantages according to the present invention are provided by a 0-10V dimming interface protection circuit generating an indication that line voltage is applied across first and second leads of the dimming interface by controlling the light output of a lamp. Preferably, the protection circuit includes a positive temperature coefficient (PTC) thermistor serially connected between a line voltage source and the first lead of the dimming interface, a voltage detector connected across the first and second leads to detect application of line voltage to the dimming interface and to generate a control signal, and a switch operated responsive to the control signal, where operation of the switch increases resistance of the PTC thermistor to thereby limit current to the dimmer interface and limit light output by the lamp.
These and other objects, features and advantages according to the present invention are provided by a 0-10V dimming interface protection circuit generating an indication that line voltage is applied across first and second leads of the dimming interface by controlling the light output of a lamp, including a first device for limiting current serially connected between a line voltage source and the first lead of the dimming interface, a second device connected across the first and second leads for detecting the application of line voltage to the dimming interface and for generating a control signal, and a third device for switching, operated in response to the control signal, for causing an increase in resistance of the first device to thereby limit current to the dimmer interface and limit light output by the lamp. According to one aspect of the invention, the protection circuit also includes a fourth device for preventing spurious operation of the second device.